Underground lab to shed light on dark matter

One kilometre under the ground, in a part of Victoria’s Stawell Gold Mine that is no longer in use, the first known dark matter laboratory in the Southern Hemisphere is preparing to join the global quest to understand the nature of dark matter and unlock the secrets of our universe.

Officially opened last week, the Stawell Underground Physics Laboratory (SUPL) is set to be the new epicentre of dark matter research in Australia. Managed by SUPL Ltd, which is co-owned by the University of Melbourne, the Australian Nuclear Science and Technology Organisation (ANSTO), the Australian National University, Swinburne University of Technology and the University of Adelaide, the lab will be home to a multidisciplinary team of scientists who will use the state-of-the-art SABRE Dark Matter Detector to ‘see’ dark matter and answer some of the biggest questions in physics.

Theorists have suggested that dark matter is an invisible and unknown substance that makes up about 85% of the mass of the universe. Amongst many puzzles, humankind’s first detection of dark matter would confirm the theory that it was dark matter particles that provided the gravitational seeds for the formation of galaxies.

The challenge is that while its effects have been observed, dark matter has remained undetected and so much about its nature is unknown. Australian scientists are using the lab and its specialist instruments to detect dark matter.

Scientists from ANSTO, which operates highly sensitive radiation detectors at Lucas Heights, advised on the extremely low background radiation environment required to operate the SABRE Dark Matter Detector. The detector includes a 2.6 x 3.1 m vessel made from radioactive-free pure steel containing a liquid scintillator; inside there are ultrapure sodium iodide detector crystals which are instrumented to observe dark matter interactions.

Photomultiplier tubes (PMTs) — light detectors capable of observing single photons — are independently coupled to both the sodium iodide crystals and the liquid scintillator, in order to sense the light emitted when different types of radiation interact with these detector elements. To potentially detect dark matter particles, the detector must be protected from all other sources of radiation, as far as possible.

“The ultrasensitive precision detectors that are being used to search for particles of dark matter require very low levels of background radiation, which is where ANSTO assisted,” said ANSTO’s Senior Advisor, Strategic Projects, Dr Richard Garrett.

“We contributed to the design of the laboratory and to the specifications and selection of materials used in its construction to ensure minimal background radiation and maximum research accuracy.

“Our elimination of background radiation will give the chief investigators confidence that any particles they detect are not something else.”

In addition to understanding dark matter, ANSTO researchers will use the lab for very sensitive measurements of environmental samples, and to investigate development of biological systems like cell cultures, in the absence of background radiation.

SUPL was constructed by Ballarat-based H.Troon, using many local contractors throughout the build. The Australian and Victorian Governments each contributed $5 million towards its construction, while the Australian Research Council awarded a $35 million grant for the development of a Centre of Excellence for Dark Matter Particle Physics, to be headquartered at the University of Melbourne.

Professor Elisabetta Barberio, Head of the Centre of Excellence, said, “We know there is much more matter in the universe than we can see.

“With the Stawell Underground Physics Laboratory, we have the tools and location to detect this dark matter. Proving the existence of dark matter will help us understand its nature and forever change how we see the universe.”

Image caption: PhD student Madeleine Zurowski with lead researcher Professor Elisabetta Barberio in the Stawell Underground Physics Lab. Image credit: Olivia Gumienny.

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